Arena Service Manual
A/D converter on the UF-Proportioning Controller board. The
signal has calibration factors applied and the result is compared to
the user-requested temperature.
The second and third thermistors are contained in the “A” and “B”
conductivity probes. The "B" thermistor is used to generate a
redundant backup high alarm and provides fine control of the
temperature. The Primary thermistor provides the primary
temperature alarm. These thermistors are also used to
temperature-compensate the conductivity measurements.
The following detailed steps occur during the dialysate
temperature control. Refer to Figure 6-1.
1. The operator enters the desired dialysate temperature
through the touch screen, and this information is sent to
Single Board Computer (SBC) via the 4-Comm (Touch
Screen) board.
2. The SBC converts the desired dialysate temperature into
the “B” thermistor temperature calibration, using the
appropriate calibration constant stored in the SRAM in the
Memory board, and sends it to the UF–Proportioning
Controller board.
Calibration of the temperature measurements is a two-point
calibration done at 32 and 40°C. The calibration procedure
results in a calibration constant for both the slope and the
offset for each temperature probe/circuit.
3. The UF-Proportioning Power Board reads the temperature
from the heater control and “B” temperature probes on a
scheduled basis (every 0.2 second for the “A” and “B”
temperatures and every 1 second for the heater control
temperature).
4. The UF-Proportioning Controller board reads and converts
into a digital signal the heater control and “B” temperature
probes signals from the UF-Prop Power board, and sends
this information to the SBC.
5. The SBC reads the “B” probe temperature from the UF-
Proportioning Controller. When the temperature is
determined to be stable, the host offsets the control
temperature by the difference between the “B” probe
temperature and the user-set control temperature.
The host-determined temperature correction is calculated
using the temperature entered by the user and the stable
“B” conductivity probe temperature. If the stable “B”
conductivity probe temperature is different from the user-
6-4 157-1278-913 Rev A
November 2003
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